A novel α,ω silyl dianionic salt.: The synthesis and characterization of remotely connected benzannulated silole monoanions

The novel dilithium salt of 1,2-bis((BPSI)(2))ethane (BPSI = 3-butyl-2-phenyl-1-silaindenyl) 4 was prepared from the reaction of 2 with 1,2-bis(chloro-BPSI) ethane 3 and characterized by NMR spectroscopy and by X-ray crystallography. It is demonstrated that dianions of silicon not only can perform stepwise reactions but also that, when a quenching reagent possesses two remote electrophilic centers, they can be attacked separately and maintain single charges on the silicon centers. The two lithium ions in 4 are eta(1)-coordinated to two remote silyl anions. NMR and X-ray data are consistent with a low degree of pi-electron delocalization in the C4Si ring.